The invention relates generally to methods and apparatus (control circuitry) for controlling a battery back-up unit (BBU) associated with a rack mounted device, under rack A.C. power outage, rack Emergency Power Off (EPO) and normal rack power down conditions. Examples of such devices include tape drives, hard discs, processors, and the like, which are typically rack mounted in general purpose digital computing systems.
More particularly, the invention relates to a device BBU control circuit which can distinguish between a rack A.C. power outage and both rack EPO and normal rack power down conditions (1) to permit the device BBU to supply device power whenever an A.C. Power outage condition exists; and (2) to deactivate the device BBU whenever either a rack EPO or normal rack power down condition exists.
Battery backed up uninterruptible power supplies are well known to those skilled in the art and are described, for example, in U.S. Pat. No. 4,675,538, issued Jun. 23, 1987, to Epstein, entitled "General Purpose Uninterruptible Power Supply". Such power supplies may have their battery back-up capability switched on during the failure of a primary power source (e.g., a commercial A.C. power source), or operated in parallel with the primary source to compensate for transients induced by, for example, noise, surges, etc.
Other types of methods and apparatus are known which rely on battery back-up capabilities to assure the continuous supply of power to (1) a system as a whole; (2) to architected system components (such as racks and other types of modules which together form a system); and (3) to individual devices included in racks. Examples of such methods and apparatus include those employed in multi-level power distribution systems, telephone networks and computing systems, several of which are taught in the issued U.S. Patents described immediately hereinafter.
In particular, U.S. Pat. No. 4,426,587, issued Jan. 17, 1981, to Nouet, entitled "Power Distribution System", describes a multi-level power supply distribution system, including a battery backed up rack level set of power supplies for providing power to the rack level of the system.
U.S. Pat. No. 5,587,640, issued May 6, 1986, to Saitoh, entitled "Cassette Type Semiconductor Memory Device", describes a cassette type memory device that includes a battery backed up RAM.
U.S. Pat. No. 4,757,505, issued Jul. 12, 1988, to Marrington et al., entitled "Computer Power System", describes a back-up computer power system that includes an auxiliary power supply which facilitates the controllable shut down of a computer so that normal operation can be resumed once the main source of power is restored.
U.S. Pat. No. 4,528,458, issued Jul. 9, 1985, to Nelson et al. entitled "Self-Diagnostic Redundant Modular Power Supply", describes a redundant modular power supply having a plurality of modules, at least one of which includes test apparatus for detecting module failures.
U.S. Pat. No. 4,691,274, issued Sep. 1, 1987, to Matouk et al., entitled "Modular Electronic Power Supply", describes a reliable modular electronic power supply adapted for use in computer systems.
U.S. Pat. No. 4,615,009, issued Sep. 30, 1986, to Battocletti et al., entitled "Electronic Energy And Power Monitoring Apparatus" and U.S. Pat. No. 4,791,362, issued Dec. 18, 1988, to Philpot, entitled "Modularized Solid State Register", describe assemblies for monitoring or metering a plurality of electrical energy and power parameters.
The aforementioned patents, which illustrate state of the art systems that include battery back-up features, including battery back-up control and monitoring systems, do not teach, claim or even suggest methods or apparatus for controlling a BBU associated with a rack mounted device under rack A.C. power outage, rack EPO and normal rack power down conditions (sometimes referred to hereinafter collectively as "rack power conditions").
The ability to effect such control based on the aforementioned rack power conditions would be desirable (1) to permit a BBU associated with a rack installed device to supply device power whenever an A.C. power outage condition exists; and (2) to deactivate the device BBU whenever either a rack EPO or normal rack power down condition exists.
Presently, rack mounted battery backed up devices (i.e., devices with a battery back-up (BBU) feature), have no way of distinguishing a rack EPO condition or normal rack power down condition, from a rack A.C. power outage condition. As a consequence, when commercially available rack enclosures (enclosures capable of housing and being connected to devices having BBU features), experience a normal rack power down or rack EPO condition, the BBUs in any battery backed up devices installed in the rack will provide device power until either being manually deactivated or depleted.
While devices themselves are known which (1) have an EPO switch and a BBU feature, and which (2) are able to distinguish between the device's EPO switch being depressed and power to the device being otherwise interrupted; such capability is not known to extend out beyond the device itself and up the system hierarchy to at least to the rack level.
Accordingly, it would be desirable to provide methods and apparatus for automatically distinguishing a rack EPO condition or normal rack power down condition, from a rack A.C. power outage condition system so that (1) rack mounted devices having a BBU feature do not have their BBUs unnecessarily drained under normal rack power down and rack EPO conditions; and (2) BBU power is permitted to energize a rack installed battery backed up device during rack A.C. power failures.
An example of a commercially available rack enclosure in which the invention would find application is the 9309 Rack Enclosure manufactured by IBM ("IBM" is a trademark owned by the International Business Machines Corporation), which is described in IBM Publication GA24-4103-04, entitled "9309 Rack Enclosure General Information And Site Preparation Guide (Models 1 And 2)", hereby incorporated by reference.
Those skilled in the art will readily appreciate that in the illustrative IBM 9309 rack enclosure there does not exist any way of communicating to devices installed in the rack that a rack level EPO condition exists or that a normal rack shut down condition exists, i.e., conditions during which it would be desirable for a given devices BBU feature to be deactivated.
Accordingly, it would also be desirable to provide methods and apparatus for performing the aforestated device BBU control function without having to redesign the rack enclosure and/or having to generate signals other than those presently used to operate the rack itself.
In fact, it would be desirable to provide to methods and apparatus which support communication of rack power conditions to the installed device level of the system hierarchy and which perform the object device BBU control function utilizing "non-specific" signals existing in a commercially available rack. The term "non-specific signals" is defined herein to mean signals that are being generated and used for purposes other than device level BBU switching in commercially available rack enclosures, such as the aforementioned illustrative IBM 9309 rack enclosure.